A 138-GHz Multimode Super-Regenerative Oscillator Radar Sensor With Quench Control in 70-nm GaAs pHEMT Technology

This article presents a 138-GHz high-sensitivity multimode super-regenerative oscillator (SRO) radar sensor implemented in a 70-nm gallium arsenide (GaAs) pseudomorphic high electron mobility transistor (pHEMT) technology. Compared to conventional Doppler radar or self-injection-locked (SIL) radar sensors, the proposed SRO design leverages periodic quench signals to trigger transient oscillation cycles, enabling substantial gain during the build-up phase for superior motion sensitivity. The sensor integrates a substrate-integrated waveguide (SIW) monopole antenna and analog envelope detection circuitry, achieving low power consumption and reduced system complexity. Through comprehensive experiments, the proposed sensor demonstrates robust vital sign detection—including respiration and heartbeat—at distances up to 1.4 m. Parametric analyses reveal that square-wave quench signals, low quench frequencies, and moderate duty cycles (e.g., 50%) yield optimal performance. Compared to its SIL counterpart implemented in the identical GaAs pHEMT technology, the SRO radar achieves >26-dB improvement. These results validate the multimode SRO-based radar architecture as a promising solution for miniaturized, high-sensitivity, noncontact biomedical sensing in indoor and clinical environments.